1. Field of the Invention
The invention relates to apparatus and methods that more efficiently fabricate thin films for use in the active components of integrated circuits, and more particularly, such apparatus and methods employing misted liquid deposition devices and techniques.
2. Statement of the Problem
The formation of thin films of complex chemical compounds such as metal oxides, ferroelectrics, materials with high dielectric constants, and so on, is very important in the integrated circuit art. It is particularly difficult to form thin films for use in active components in integrated circuits; that is, components that perform an electrical function, such as charge storage or control, as opposed to materials that merely serve as temporary sacrificial layers or insulation or protective packaging for an integrated circuit. This difficulty arises from the fact that even minor microscopic defects can result in the loss of an entire device, and thus significantly decrease the yield and increase the cost of producing integrated circuits. Thus, the art of fabricating thin films for active components is a highly developed art with much ongoing research.
Some methods of forming thin films of complex chemical compounds for integrated circuits are: physical vapor deposition (PVD) techniques, such as thermal, electron beam, molecular beam epitaxy, laser ablation and sputtering; chemical vapor deposition (CVD); and misted deposition. See, for example, U.S. Pat. No. 5,648,114 issued Jul. 15, 1997, and U.S. Pat. No. 5,456,945 issued Oct. 10, 1995. All of these methods are used in commercial manufacturing systems, though they each have significant disadvantages. PVD techniques typically require a deposition environment of medium vacuum (.about.10.sup.-3 to 25 torr), high vacuum (.about.10.sup.-7 to 10.sup.-3 torr), or very high vacuum (.about.10.sup.-12 to 10.sup.-7 torr) to create or maintain an evaporate vapor, to prevent contamination from atmospheric gases, and/or to create sub-micron thin films. Such vacuums can be costly to create and maintain, and the corresponding vacuum pumps themselves have the potential of introducing contaminants (such as oil) into the deposition chambers unless additional preventative measures are introduced. Further, the physical necessity of pumping the vacuum chambers to the corresponding operating range and waiting until the interior surfaces have completed outgasing the residual atmospheric gases can take from several hours to several days. Such costs and delays reduce the efficiency and, hence, the commercial value of large-scale PVD manufacturing. Although CVD can operate at low vacuum (.about.25 to 760 torr), CVD requires transport of the precursors of the material desired to be deposited via chemically reactive carrier gases. The chemical reactions or decompositions that result in the desired deposition also frequently create exhaust products that are toxic or corrosive, which then require additional procedures (typically involving scrubbers) to prevent their release into the atmosphere. Further, CVD requires cleaning of the deposition chamber on a frequent and regular basis to maintain high quality of the thin films subsequently fabricated in the same chamber. As in PVD techniques, such encumbrances erode the efficiency of large-scale manufacturing by CVD. Misted deposition devices and processes in the prior art operate at low vacuum and do not require the maintenance of CVD devices, but are not suited to large-scale manufacturing since only one wafer can be fabricated at a time. Thus, an apparatus and method for producing thin films for use in active components in integrated circuits that is capable of sustained continuous or semi-continuous production that is easy and relatively cheap to maintain, produces a finished and consistently high quality thin film, permits a shorter production time, and results in high yields of integrated circuit chips would be highly desirable.